docs: def _find_secondary_anchors(self,  residue,  heavy_atom,  anchor):
          """
          Searches through the bond network for atoms bound to the anchor.
          Returns a secondary and tertiary anchors.
          Example,  for CA,  returns C and O.
          """
          
          for secondary in self.bonds[residue][anchor.name][1]:
              for tertiary in self.bonds[residue][secondary.name][1]:
                  if (tertiary.name != heavy_atom.name 
                      and tertiary.name != anchor.name):
                      
                      return (secondary,  tertiary)
          
          return None